Development,Characterization,and Application of a Double-Waveguide Evanescent Sensor

A double-waveguide evanescent sensor has been developed and characterized. A fraction of the evanescent field (λ _e = 488 nm) generated at the core (n_c = 1.48)/cladding (n_cl = 1.45) interface of a glass optical fiber penetrates into the cladding and the polymeric jacket (n_j = 1.54) coated onto the cladding. Fluorescence is excited within the jacket and, due to the higher refractive index of the jacket, the emission is totally internally reflected within it. The emission (λ _em = 605 nm) has been collected with the use of lateral and front-end geometries. The sensor has been used to determine iodine in gas and liquid phases using an indirect approach. Iodine reacts with unsaturated sites of the polymer and absorbs the fluorescence, causing a reduction in the fluorescence background. The rate of fluorescence reduction is proportional to the concentration or partial pressure of iodine in the sample.